The body has the capacity to compensate for an occluded artery by creating a natural bypass upon increased fluid shear stress. How this mechanical force is translated into collateral artery growth (arteriogenesis) is unresolved. We show that extravasation of neutrophils mediated by the platelet receptor GPIbα and uPA results in Nox2-derived reactive oxygen radicals, which activate perivascular mast cells. These c-kit(+)/CXCR-4(+) cells stimulate arteriogenesis by recruiting additional neutrophils as well as growth-promoting monocytes and T cells. Additionally, mast cells may directly contribute to vascular remodeling and vascular cell proliferation through increased MMP activity and by supplying growth-promoting factors. Boosting mast cell recruitment and activation effectively promotes arteriogenesis, thereby protecting tissue from severe ischemic damage. We thus find that perivascular mast cells are central regulators of shear stress-induced arteriogenesis by orchestrating leukocyte function and growth factor/cytokine release, thus providing a therapeutic target for treatment of vascular occlusive diseases.

Hypoxia promotes vascularization by stabilization and activation of the hypoxia inducible factor 1α (HIF-1α), which constitutes a target for angiogenic gene therapy. However, gene therapy is hampered by low gene delivery efficiency and non-specific side effects. Here, we developed a gene transfer technique based on magnetic targeting of magnetic nanoparticle-lentivirus (MNP-LV) complexes allowing site-directed gene delivery to individual wounds in the dorsal skin of mice. Using this technique, we were able to control HIF-1α dependent wound healing angiogenesis in vivo via site-specific modulation of the tyrosine phosphatase activity of SHP-2. We thus uncover a novel physiological role of SHP-2 in protecting HIF-1α from proteasomal degradation via a Src kinase dependent mechanism, resulting in HIF-1α DNA-binding and transcriptional activity in vitro and in vivo. Excitingly, using targeting of MNP-LV complexes, we achieved simultaneous expression of constitutively active as well as inactive SHP-2 mutant proteins in separate wounds in vivo and hereby specifically and locally controlled HIF-1α activity as well as the angiogenic wound healing response in vivo. Therefore, magnetically targeted lentiviral induced modulation of SHP-2 activity may be an attractive approach for controlling patho-physiological conditions relying on hypoxic vessel growth at specific sites.

Background Sepsis, the most severe form of infection, involves endothelial dysfunction which contributes to organ failure. To improve therapeutic prospects, elucidation of molecular mechanisms underlying endothelial vascular failure is of essence. Methods Polymicrobial contamination induced sepsis mouse model and primary endothelial cells incubated with sepsis serum were used to study SHP-2 in sepsis-induced endothelial inflammation. SHP-2 activity was assessed by dephosphorylation of pNPP, ROS production was measured by DCF oxidation and protein interactions were assessed by proximity ligation assay. Vascular inflammation was studied in the mouse cremaster model and in an in vitro flow assay. Findings We identified ROS-dependent inactivation of the tyrosine phosphatase SHP-2 to be decisive for endothelial activation in sepsis. Using in vivo and in vitro sepsis models, we observed a significant reduction of endothelial SHP-2 activity, accompanied by enhanced adhesion molecule expression. The impaired SHP-2 activity was restored by ROS inhibitors and an IL-1 receptor antagonist. SHP-2 activity inversely correlated with the adhesive phenotype of endothelial cells exposed to IL-1β as well as sepsis serum via p38 MAPK and NF-κB. In vivo , SHP-2 inhibition accelerated IL-1β-induced leukocyte adhesion, extravasation and vascular permeability. Mechanistically, SHP-2 directly interacts with the IL-1R1 adaptor protein MyD88 via its tyrosine 257, resulting in reduced binding of p85/PI3-K to MyD88. Interpretation Our data show that SHP-2 inactivation by ROS in sepsis releases a protective break, resulting in endothelial activation. Fund German Research Foundation, LMU Mentoring excellence and FöFoLe Programme, Verein zur Förderung von Wissenschaft und Forschung, German Ministry of Education and Research.

Double-stranded DNA (dsDNA) constitutes a potent activator of innate immunity, given its ability to bind intracellular pattern recognition receptors during viral infections or sterile tissue damage. While effects of dsDNA in immune cells have been extensively studied, dsDNA signalling and its pathophysiological implications in non-immune cells, such as the vascular endothelium, remain poorly understood. The aim of this study was to characterize prothrombotic effects of dsDNA in vascular endothelial cells. Transfection of cultured human endothelial cells with the synthetic dsDNA poly(dA:dT) induced upregulation of the prothrombotic molecules tissue factor and PAI-1, resulting in accelerated blood clotting in vitro, which was partly dependent on RIG-I signalling. Prothrombotic effects were also observed upon transfection of endothelial cells with hepatitis B virus DNA-containing immunoprecipitates as well human genomic DNA. In addition, dsDNA led to surface expression of von Willebrand factor resulting in increased platelet-endothelium-interactions under flow. Eventually, intrascrotal injection of dsDNA resulted in accelerated thrombus formation upon light/dye-induced endothelial injury in mouse cremaster arterioles and venules in vivo. In conclusion, we show that viral or endogenous dsDNA induces a prothrombotic phenotype in the vascular endothelium. These findings represent a novel link between pathogen- and danger-associated patterns within innate immunity and thrombosis.

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